If you go over 4 players, please run dedicated. Your players will thank you.

If you have less than 1Mb upload, don't run more than 4 players. Your players will thank you for that, too.

The engine consumes bandwidth pretty heavily, so you are best off running servers only if you really know you have the upload bandwidth (remember that even if you have a 3Mb Cable Modem, your upload is still going to be something pretty subpar. For hosting, your upload is far more important than download.)